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参数资料
| 型号： | NCP5425DBG |
| 厂商： | ON Semiconductor |
| 文件页数： | 18/22页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 20TSSOP |
| 标准包装： | 75 |
| PWM 型： | 电压模式 |
| 输出数： | 2 |
| 频率 - 最大： | 938kHz |
| 占空比： | 100% |
| 电源电压： | 4.75 V ~ 13.2 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | 0°C ~ 125°C |
| 封装/外壳： | 20-TSSOP（0.173"，4.40mm 宽） |
| 包装： | 管件 |
NCP5425
Given an ESR value of 3.5 m W , the current limit becomes
20 A. If an increased current limit is required, a resistor
divider can be added (see Figure 8). Advantages of setting
the current limit by using the winding resistance of the
inductor (relative to a sense resistor) are higher efficiency
Master
Switch
Node
Slave
Error
Amp
Slave
Switch
Node
and lower heat generation. The tolerance of the inductor
ESR must be factored into the design of the current limit.
Lx
R1
R2
Lx
Finally, one or two more components are required for this
approach than with resistor sensing.
Rx
C1
C1
Rx
Selecting and Configuring Current Sharing for a 2
Phase Single Output Application
When the two controllers are connected as a single output
two phase Buck Converter, they are in a Master?Slave
configuration. The Slave controller on the right side of
Figure 6 tries to follow information provided by the Master
controller, on the left. This circuit uses inductor current
sensing, in which the parasitic resistances (LSR) of the
R3
DC
Output
Figure 12. 40%/60% Current Sharing
controllers’ output chokes are used as current sensing
elements. On the Slave side (Controller Two), both Error
Amplifier inputs are brought to external pins so the
Master
Switch
Node
Slave
Switch
Node
reference is available. The RC network in parallel with the
output inductor on the Master side (Controller One)
generates the reference for the Slave. Current information
from the Slave is fed back to the error amplifier ’s inverting
Lx
R2
Slave
Error
Amp
R1
Lx
input. In this configuration, the Slave tries to adjust its
current to match the current information fed to its reference
input from the Master Controller. If 50?50 current sharing
Rx
C1
C1
Rx
is needed, then Figure 8a is used for both sides to generate
the reference and the inverting signals. The values for both
sides should be calculated with the following equation:
R3
R1 +
Lx
C1 · Rx
, where,
DC
Output
L x = Inductor value, both controllers should use the same
inductor.
R x = Internal resistance of L, from the inductor data sheet.
C1 = Select a value such that R1 is less than 15 K W .
With the RC time constant selected to equal the L x /R x time
constant, the voltage across the capacitor will be equal to the
voltage drop across the internal resistance of the inductor.
For proper sharing, the inductors on both Master and Slave
side should be the identical.
If a current share ratio other than 50?50 is desired,
inductor sense resistor network selection is a three step
process:
1. Decide how the total load current will be budgeted
between the two controllers.
2. Calculate the value of R1 for the controller with
the lesser current share.
3. Calculate the current sense resistor network
(2 resistors) for the controller with the greater
current share.
Figure 13. 66.7%/33.3% Current Sharing
Example 1
Assume we have elected to source 40% of the output
current from the master controller, and 60% from the Slave.
Figure 12 shows the configuration of the inductor sense
networks and Slave error amplifier. The ratio of
Slave?to?Master load current is 60%/40%, or 1.5:1. R2 and
R3 must be chosen to satisfy two conditions:
A parallel equivalent resistance equal to R1, and,
A ratio such that the drop across the parasitic resistance of
the Slave inductor is 1.5 times the drop across the parasitic
resistance of the Master inductor when the inputs to the
Slave error amplifier are equal (assumes the inductors are
identical). The optimum value of R1 is described by the
equation:
R1 + Lx (C1 * Rx)
In the two examples that follow, the inductor sense
resistors are designated R1, R2, and R3, as depicted in
Figures 12 and 13.
http://onsemi.com
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